The invention relates to an apparatus for continuously casting metal melt, preferably steel melt, to form cast strip.
When steel is being cast in two-roll casting machines, there are in each case two internally cooled casting rolls which rotate in opposite directions during the casting process, are arranged axially parallel and delimit the longitudinal sides of a casting gap formed between them. The casting gap is sealed laterally by side plates which are placed against the end sides of the casting rolls. In each case sufficient liquid melt for a melt pool to form above the casting gap is cast into this casting gap. Melt which passes out of this melt pool onto the casting rolls solidifies there and is conveyed into the casting gap by the casting rolls. The cast strip is formed in the casting gap from the strand shells formed in this way on the casting rolls and from melt which is still liquid, and this cast strip is then drawn off at the bottom of the casting gap and fed for further processing.
Since the cast strip is at high temperatures when it leaves the casting gap, scale forms on its surface on contact with oxygen, which represents a difficulty for the continuous further processing of the strip. In particular, the scale has an adverse effect on the working result of the in-line hot-rolling which is carried out after the strip has been cast.
Various solutions have been proposed for the purpose of reducing the extent to which scale is formed. For example, it is known from U.S. Pat. No. 5,584,337, EP-A 776 984, EP-A 780 177 and EP-B 830 223 to arrange a housing in which a reduced-oxygen, inert gas atmosphere is maintained during casting operation beneath the casting gap in apparatuses of the type in question. In particular, it is also known from EP-A 780 177 to move the housing directly onto the housing and to produce an airtight contact by means of a touching seal.
In addition to the problem of scale formation, a further difficulty when the known two-roll casting machine is operating is that the thermal radiation emitted from the cast strip leads to considerable heating of the components of the two-roll casting machine which are within the region of the radiation. This heating leads, on the one hand, to deformation of the carriers which carry the casting rolls. This deformation makes it difficult to ensure dimensional accuracy of the cast strip in particular if the corresponding carriers are designed as a movable frame to allow the casting rolls to be changed. On the other hand, the high temperatures in the region of the two-roll casting machine lead to considerable physical loading on the staff monitoring casting operation on the casting floor.
Furthermore, the direct thermal radiation of the very hot strip emerging from the casting gap reduces the extent to which the casting-roll surface can be rapidly cooled, and the casting-roll surface also becomes soiled by dirt particles which may be present in the upwardly flowing hot gas masses beneath the two casting rolls.
In particular in the event of the casting rolls being changed as a result of a format change, with predominantly the strip width of the strip to be cast and therefore the dimension of the casting rolls (diameter, surface length) being altered, the geometric conditions for entry of the cast strip into the housing arranged immediately downstream also change. This also results in the need to change parts of this housing, thereby significantly increasing the time required for the format change.